U.S. patent number 6,979,496 [Application Number 10/887,569] was granted by the patent office on 2005-12-27 for mill blank library and computer-implemented method for efficient selection of blanks to satisfy given criteria.
This patent grant is currently assigned to D4D Technologies, LP. Invention is credited to Jorey A. Chernett, Howard Frysh, Basil A. Haymann, Henley S. Quadling, Mark S. Quadling.
United States Patent |
6,979,496 |
Haymann , et al. |
December 27, 2005 |
Mill blank library and computer-implemented method for efficient
selection of blanks to satisfy given criteria
Abstract
The present invention relates generally to mill blank
constructions to facilitate the manufacture of dental restorations.
A given mill blank is formed in a shape (i.e. with a given
geometry) that has been predetermined to reduce material waste when
the mill blank is machined into the final part. A set of two or
more blanks each having such characteristics comprise a smart blank
"library." In one embodiment, a smart blank library includes a
sufficient number of unique blanks such that, when the geometry of
the designed restoration is known, the smart blank with a highest
yield can be selected for use in milling the restoration. The
"yield" of a given smart blank represents the amount of material of
the smart blank that is actually used in the final restoration.
Automated processes for smart blank inventory management and smart
blank selection are also described.
Inventors: |
Haymann; Basil A. (Dallas,
TX), Quadling; Mark S. (Plano, TX), Quadling; Henley
S. (Addison, TX), Frysh; Howard (Dallas, TX),
Chernett; Jorey A. (Plano, TX) |
Assignee: |
D4D Technologies, LP
(Richardson, TX)
|
Family
ID: |
34079170 |
Appl.
No.: |
10/887,569 |
Filed: |
July 9, 2004 |
Current U.S.
Class: |
428/542.8;
433/201.1; 433/229; 433/223 |
Current CPC
Class: |
A61C
13/0004 (20130101); A61C 13/0003 (20130101); A61C
5/77 (20170201); A61C 13/0022 (20130101) |
Current International
Class: |
A61C 013/00 ();
A61C 013/08 (); A61C 013/113 () |
Field of
Search: |
;433/167,171,201.1,206,202.1,208,212.1,213,215,223,218,226,229
;241/24.1,24.12,24.25 ;428/542.8 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
VITA CEREC(R) Produkte/Products, Nov. 2000 (Edition),
Germany..
|
Primary Examiner: Lavilla; Michael E.
Attorney, Agent or Firm: Judson; David H.
Parent Case Text
This application is based on and claims priority from Provisional
Patent Application Ser. No. 60/485,935, filed Jul. 9, 2003.
Claims
Having now described our invention, what we claim is as
follows:
1. A method of assembling blanks for use in manufacturing dental
restorations, comprising: given a set of blanks, selecting an
assemblage of the blanks, wherein at least first and second of the
blanks in the assemblage comprise a body adapted to be shaped by
material removal, the body of the first blank having a geometry
that differs from the body of the second blank by other than
scaling, and wherein the body of each of the first and second
blanks has at most one symmetric plane; and using that assemblage
to manufacture dental restorations.
2. The method as described in claim 1 wherein the assemblage of the
blanks is selected to maximize an average yield per blank, wherein
the average yield per blank is calculated as a weight of a finished
restoration divided by a weight of a blank prior to being shaped by
material removal.
3. The method as described in claim 2 wherein the average yield per
blank is a weighted average.
4. The method as described in claim 1 wherein the assemblage of the
blanks is selected to balance an average yield per blank with a
productivity factor.
5. The method as described in claim 1 wherein the assemblage of the
blanks is selected to balance an average yield per blank with a
cost factor.
6. The method as described in claim 1 wherein the assemblage of the
blanks is selected to balance a set of yield, productivity, cost
and tooth distribution factors.
7. An assemblage, comprising: a plurality of mill blanks, at least
first and second of the mill blanks in the plurality each
comprising a body adapted to be shaped by material removal; wherein
the body of the first blank has a geometry that differs from the
body of the second blank by other than scaling; wherein the body of
each of the first and second blanks has at most one symmetric
plane.
8. The assemblage as described in claim 7 wherein each blank
includes a holder to enable the blank to be maintained within a
shaping apparatus.
9. The assemblage as described in claim 7 wherein at least one of
the blanks is formed of a metal or metal alloy.
10. The assemblage as described in claim 7 wherein at least one of
the blanks is formed of a ceramic.
11. A method of producing dental items, comprising: maintaining an
assemblage of "m" mill blanks, the assemblage comprising at least
first and second mill blanks each comprising a body adapted to be
shaped by material removal, wherein the body of the first blank has
a geometry that differs from the body of the second blank by other
than scaling, and wherein the body of at least one of the mill
blanks in the assemblage has at most one symmetric plane; for a
given restoration R being designed, selecting a subset {B.sub.1,
B.sub.2, . . . B.sub.n,) of "n" blanks, where n.ltoreq.m, such that
each of the blanks of the subset contain the restoration R; and
selecting a given one of the blanks of the subset for use in
producing the restoration.
12. The method of claim 11 wherein the given one of the blanks that
is selected has the smallest volume.
13. The method of claim 11 wherein the given one of the blanks that
is selected has a minimal volume difference with respect to the
given restoration R being designed.
14. The method of claim 11 wherein the dental item is prepared by
milling the selected blank.
15. The method as described in claim 14 wherein the selected blank
is milled using a computer-assisted milling machine.
Description
BACKGROUND OF THE INVENTION
1. Technical Field
This invention generally relates to a system for preparing dental
prostheses. In particular, the invention relates a smart mill blank
library and preparing dental prostheses for use as crowns, onlays,
inlays, veneers, bridges, and other restorations from a mill blank
selected from a mill blank library.
2. Related Art
The art of fabricating custom-fit prosthetics in the dental field
is well-known. Prosthetics are replacements for tooth or bone
structure. They include restorations, replacements, inlays, onlays,
veneers, full and partial crowns, bridges, implants, posts, and the
like. Typically, a dentist prepares a tooth for the restoration by
removing existing anatomy, which is then lost. The resultant
preparation may be digitized or a dental impression is taken, for
the purpose of constructing a restoration. The restoration may be
constructed through a variety of techniques including manually
constructing the restoration, using automated techniques based on
computer algorithms, or a combination of manual and automated
techniques. In one known technique, the prosthetic is fabricated
using a computer-assisted (CAD/CAM) system, such as a
computer-aided milling machine. One such machine is the CEREC 3D
system from Sirona Dental Systems. Computer-aided machines of this
type work by shaping the prosthetic from mill blanks. A mill blank
is a solid block of material from which the prosthetic is shaped by
a shaping apparatus whose movements are controlled by the computer.
Under computer control, the size, shape, and arrangement of the
restoration may be subject to various physical parameters,
including neighboring contacts, opposing contacts, emergence angle,
and color and quality of the restoration to match the neighboring
teeth.
A common restoration includes a porcelain-fused-to-metal (PFM)
crown. The crown typically comprises a cap of porcelain material
overlayed on a thin metal coping. The metal coping forms an
interface between the preparation and the porcelain material.
Common restorations typically include a coping formed from precious
or semi-precious metals, including gold or a gold alloy. The
material may be selected based on the color and various other
properties to optimize a long-lasting natural looking
restoration.
The copings or full metal crowns typically are formed from a lost
wax casting process. The process may include placing several wax
copings on a wax tree, which is connected to a wax base. The
structure is placed in a cylinder with investing material, and the
wax is melted out after the investing material has set. A molten
metal, typically a gold alloy, is then poured into the remaining
structure, and the entire cylinder is placed into a centrifuge to
distribute the molten material to a uniform distribution.
Preferably, the alloy base and the tree are recovered for use in a
future casting process. The continued re-melting of the gold alloy
along with other contaminants, however, introduces oxidation and
other tarnishing agents into the gold alloy.
Other methods for forming the coping may be used, including milling
or machining with some kind of block or blank, but these techniques
may waste much of the metal material. The ratio of the volume of
the final metal coping to the volume of a typical enclosing mill
blank (a symmetric block or cylinder) is often very small such that
much of the material may be wasted. As noted above, a common
milling process includes forming the coping from a mill blank using
a computer-assisted milling machine. The blank includes a
sufficiently large rigid attachment so that it may be held solidly
while the machining process is underway. A rectangular or
cylindrical blank is commonly used, and the vast majority of
material is removed via the machining process. U.S. Pat. No.
4,615,678 to Moermann et al. discloses a conventional mill blank of
this type made of ceramic silica material. There are, of course,
numerous other types of mill blanks available commercially.
The cost of recovering the wasted material often exceeds the cost
of the material sought to be recovered. The object may be milled
using a wet milling process, which typically results in the
discarded material (including fine particles) being mixed with
water or other cutting fluids. This is not a significant concern
when the restoration is being formed using inexpensive materials;
however, when utilizing expensive materials, such as gold, the
issue of dealing with the recovery of the machined material may
make the process prohibitively expensive. Indeed, the cost of the
discarded materials in the case of precious or semi-precious
materials is the single most important reason that prior art
techniques have proven to be undesirable or cost prohibitive.
Additional concerns are the time required to cut through the
discarded material, as well as the additional wear and tear on the
tools.
There have been a few incidental suggestions in the art to address
this problem. Thus, for example, U.S. Pat. No. 4,615,678 teaches
that the body portion of a mill blank can be formed in a way to
minimize wear on and run time of the milling machine by being
shaped initially to more closely resemble the final implant. An
illustrative example is a blank for use in forming a two lobed
inlay that includes a transverse groove in one side thereof. U.S.
Published Patent Application 2003/0031984 to Rusin et al.
illustrates a similar blank construction, and it further notes that
blanks can come in a variety of shapes and sizes.
While these suggestions are useful, there remains a need in the art
to provide improved mill blank configurations and assemblages that
facilitate prosthetic milling operations in a manner to reduce
material waste, reduce machining time, and to increase value.
BRIEF SUMMARY OF THE INVENTION
It is an object of the present invention to provide improved mill
blank constructions to facilitate the manufacture of dental
restorations. In general, this object is achieved by providing a
given mill blank in a shape (i.e. with a given geometry) that has
been predetermined to reduce material waste when the mill blank is
machined into the final part. A mill blank that has been
intelligently pre-configured into a form that more closely
resembles the final dental part is sometimes referred to as a
"smart" blank.
It is a further object of the invention to provide such mill blanks
in a collection or "assemblage." A set of two or more smart blanks
each having such characteristics is also sometimes referred to as a
smart blank "library." In a preferred embodiment, it is desirable
to provide a smart blank library that includes a sufficient number
of unique blanks such that, when the geometry of the designed
restoration is known, the smart blank with a highest yield can be
selected for use in milling the restoration. The "yield" of a given
smart blank represents the amount of material of the smart blank
that is actually used in the final restoration, with the higher the
yield value meaning the closer the "fit" of the smart blank to the
designed restoration. In a particular embodiment, a smart blank
library is maintained with a given number of unique blanks so as to
balance an average yield per smart blank with a goal of satisfying
an inventory requirement for the library (e.g., the smallest
possible library size necessary to meet anticipated production
requirements over a given time period). In this embodiment, it is
desirable to have a sufficient number of unique smart blanks in the
library such that the smart blank with a highest average yield can
be selected and is available for use while ensuring that the number
of blanks remains within a given inventory production factor.
According to a more specific embodiment, an assemblage of blanks
comprises at least first and second smart blanks, with each smart
blank adaptable for producing a formed part that can be used for
replacement or restoration of one or more teeth by removing as
little material from the blank as possible (i.e., an optimize
yield). The first blank has a first geometry, and the second blank
has a second geometry that differs from the first geometry other
than by mere scaling. The first blank is configured to resemble a
first given restoration, and the second blank is configured to
resemble a second given restoration. Each of the blanks further
includes a holder (a sprue) for mounting the blank in a shaping
apparatus. The blank comprises a precious or semi-precious
material, a ceramic silica material, or other material suitable for
the substructure or final restoration.
It is another more general object of the invention to provide a
smart mill blank library that comprises multiple smart mill blanks
having a variety of predetermined shapes, sizes, and arrangements.
Preferably, a given smart mill blank in the library is pre-formed
to a target size, shape and arrangement so that the library as a
whole is useful across for a particular set of applications. Thus,
depending on the type and nature of the restoration, a particular
smart mill blank is selected from the library and used in the
milling operation. As a result, the amount of material needed to be
removed from the mill blank is reduced greatly. This is especially
desirable and cost-effective when precious or semi-precious
materials (such as gold) are being used in the restoration. Indeed,
use of a smart blank pre-formed from gold significantly reduces the
amount of gold to be recovered, in many cases reducing it to less
than that in a common lost wax casting process. In addition, the
amount of time to machine the restoration is reduced due to a
relatively small amount of material that needs to be removed from
the smart mill blank. The use of such blanks provides further
process advantages including, without limitation, reducing spoiling
effects such as gold alloy tarnishing, eliminating trace metal
oxidation, and the like.
Another more general object of the present invention is to provide
a smart blank library that achieves maximum yield, so as to
minimize material waste.
According to a specific feature of the present invention, the smart
blank library comprises a set of copings or full contour crowns. A
coping is the substructure of a crown. The general shape of a
coping has an upper surface and a lower surface. The upper surface
is generally a convex surface and the lower surface is generally a
concave surface. The lower surface is configured to be able to be
affixed to a dental preparation and to form a tight seal at a
margin having a small but definite gap for cement. The general
shape of the lower surface may mirror or correspond to the shape of
a typical preparation. The general shape of the upper surface of
the coping may correspond to an occlusal surface of a particular
dental item. A selection of a smart mill blank from the library
provides a more effective way to prepare a dental prosthesis and
dental item to maintain optimal porcelain or other surface material
on top of the metal coping.
In a common restoration, such as a porcelain-on-metal crown, it is
desirable for longevity of the restoration to provide a
substantially constant thickness of the porcelain material.
Maintaining the constant thickness may reduce a risk of fracturing
the material. Accordingly, in one embodiment, the smart mill blanks
in the library may have a generally concavo-convex shape, with the
top surface having a shape that allows the porcelain-sculpted
anatomy to exhibit a near constant thickness
Other methods, features and advantages of the invention will be, or
will become, apparent to one with skill in the art upon examination
of the following figures and detailed description. It is intended
that all such additional methods, features and advantages be
included within this description, be within the scope of the
invention, and be protected by the following claims.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention may be better understood with reference to the
following drawings and its accompanying description. Unless
otherwise stated, the components in the figures are not necessarily
to scale, emphasis instead being placed upon illustrating the
principles of the invention. Moreover, in the figures, like
referenced numerals designate corresponding parts throughout the
different views.
FIG. 1 illustrates a smart blank library according to an embodiment
of the present invention;
FIG. 2 illustrates another embodiment of the invention where the
smart blank library has been sized to satisfy a given yield,
productivity, cost or other factor;
FIG. 3 illustrates a computer system that may be used to facilitate
selection of a smart blank from the library of FIG. 2,
FIG. 4 illustrates how a first restoration is tested against a set
of smart blanks in a given library to determine whether the
restoration is containable therein;
FIG. 5 illustrates how a second restoration is tested against the
set of smart blanks in the given library of FIG. 4 to determine
whether the restoration in containable therein;
FIG. 6 illustrates the smart blanks selected for use in the
manufacture of the first and second restorations;
FIG. 7 illustrates conventional mill blanks each having a large
amount of material that is discarded when the respective blank is
shaped in a prior art milling process;
FIG. 8 illustrates a pair of smart mill blanks each having a shape
and arrangement that closely approximates a final shape of a
respective coping or crown;
FIG. 9A illustrates a smart mill blank library of multiple mill
blanks that may be selected based on size, shape and arrangement of
the mill blank for the purposes of producing a coping; and
FIG. 9B illustrates a smart mill blank library of multiple mill
blanks that may be selected based on size, shape and arrangement of
the mill blank for the purposes of producing a full crown.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
For illustrative purposes, the following terms may be afforded the
following meanings in the context of the present invention:
A "blank" is a part adapted for use in custom fabrication of a
dental restoration. Typically, a blank comprises a body for being
shaped by material removal, and a holder (a "sprue") for mounting
the blank in a shaping apparatus such as a CAD/CAM (or other)
milling machine, device or system.
A "smart blank" is a blank that has been pre-configured into a form
that, as compared to a conventional blank, much more closely
resembles a restoration being designed.
A "yield" of a smart blank is the amount of material of the body
part that ends up being useful for the restoration during the
milling of the blank. According to the present invention, it is
desirable to maintain a library of smart blanks such that, in use,
an optimized yield per blank (and, thus, an optimized yield across
the library as whole) is obtained.
A "library" (or "collection," or "assemblage") of smart blanks is a
set of two or more smart blanks, with each blank adaptable for
producing a formed part that can be used for replacement or
restoration of one or more teeth, preferably by removing as little
material from the blank as possible (i.e., to optimize yield per
blank). Preferably, at least a first blank has a first geometry,
and the second blank has a second geometry that differs from the
first geometry by other than scaling. FIG. 1 illustrates a library
100 comprised of two blanks 102 and 104 that meet this
criteria.
A "restoration" refers generically to a crown, coping, bridge,
onlay, inlay, framework, or other dental item.
An "average yield per blank" is an average yield per blank,
calculated as a weight of a finished restoration divided by a
weight of an initial smart blank. Thus, e.g., if a milled coping
weighs 1.5 penny weights and the smart blank (pulled from the
library) weighs 3.0 penny weights), the average yield for this
blank is 50%.
A "size" of the smart blank library refers to the number of unique
smart blanks in the library.
A "production period" is an average number of restorations produced
within a given dental laboratory or office over a given period
(e.g., daily, weekly, monthly, or the like).
An "inventory over production factor" is the surplus, or amount of
inventory that exceeds an average production for a given production
period. Thus, assume the production period is daily. If a
laboratory fabricates 40 restorations per day (200 per week) and 80
smart blanks per day (400 per week) are needed to fulfill
production requirements, the inventory over production factor is
100%. A laboratory should have sufficient smart blanks to satisfy
its production requirements for some specified period of time.
An "intrinsic cost of the average restoration" is the cost of the
raw material used to create the finished restoration such as a
coping.
A "distribution by tooth number" is a weighted distribution based
upon laboratory productivity by tooth type (e.g., 27% 3.sup.rd
molar, 22%, 2.sup.nd molar, 11%, 1.sup.st molar, 14%, 2.sup.nd
bicuspid, 12%, 1.sup.st bicuspid, and the like).
An "average scrap per smart blank" is one minus the average yield
per smart blank.
A "scrap factor" is 100% divided by the average yield per smart
blank. Thus, for example, if the average yield per smart blank is
50%, the scrap factor is 2.0).
A "cost per restoration" is the scrap factor times the intrinsic
cost of the average restoration.
As noted above, FIG. 1 illustrates a smart blank library 100 that
comprises at least a first smart blank 102, and a second smart
blank 104. Each blank comprises a body 106 for being shaped by
material removal, and a holder 108 for mounting the blank in a
shaping apparatus. Preferably, the body 106 has a given geometry
that will closely resemble a given restoration under design.
Although not meant to be taken by way of limitation, preferably the
body of a given smart blank has, at most, one symmetric plane. In
this illustrative embodiment, the given geometry of the body of the
first smart blank 102 differs from the given geometry of the body
of the second smart blank 104 by other than scaling. The body may
be formed of any suitable blank material including, without
limitation, a precious metal or metal alloy, a semi-precious metal
or metal alloy, a ceramic or other inorganic non-metallic material,
or the like. The body is adapted to be formed or milled into any
type of restoration (or other dental prosthetic) by hand or by a
milling machine, such as a machine that uses a CAD/CAM system. Any
convenient cutting technique can be used for this purpose.
More generally, a smart mill blank library comprises a plurality of
smart mill blanks. The smart mill library includes a set of smart
blanks having a pre-formed size shape and arrangement that
approximates dental crown of various known tooth types and common
dental preparations. The library may also include a set of smart
mill blanks having a size, shape and arrangement that approximates
copings for various types of teeth and common preparations.
FIG. 2 illustrates a smart library 200 as it is maintained in a
given dental laboratory or office. It is assumed that this library
has been drawn from a larger, global set of available smart blanks
(a set that could be quite large in size theoretically given the
variations in smart blank shapes). It is further assumed that the
given dental laboratory or office only desires to maintain an
inventory of smart blanks for which it expects to have demand
and/or that satisfy some other inventory requirements. To this end,
it is a further feature of the present invention to provide or
maintain a smart blank library 200 of "n" smart blanks (as
illustrated in the figure by a library of eight (8) smart blanks
201-208), where the library 200 has a smallest possible "size" (not
necessarily of size 8, as illustrated) to satisfy a given criteria.
One such criterion simply is the average yield per smart blank, as
defined above. According to this example, the smart blank library
200 is sized with a set of unique blanks so that, when the geometry
of the designed restoration is calculated or known (the particular
technique by which this is done is not part of the present
invention), an operator is provided with an indication of which
smart blank to use, namely, the smart blank that offers the highest
yield. In this example, this is the blank that is "closest" to the
designed restoration, i.e., the blank with the least amount of
material to be removed to satisfy the given design under
construction.
Thus, in one embodiment, the smart blank library is stocked by
selecting an assemblage of the blanks that satisfy a given
criterion, where the given criterion is a maximum average yield per
blank, and the smart blanks are then used to manufacture dental
restorations. As an alternative, the given criterion is that a
weighted average of the blank yields in the assemblage is
maximized. Still another alternative criterion is that a weighted
average of the blank yields in the assemblage is maximized. Another
alternative criterion balances an average yield per blank with a
given productivity factor. A further variant would be to use a
criterion that balances an average yield per blank with a given
cost factor. Yet another given criterion balances among any of a
set of yield, productivity, cost and/or tooth distribution factors,
as more particularly described in the following paragraph by way of
some specific examples.
One possibility to determine the library size is to use a given
criterion that the average yield per smart blank be greater than a
given selectable value for a given number of restorations for a
given tooth (or tooth group), e.g., select a blank that results in
at least a 70% yield for 80% of the restorations for a given tooth.
The distribution by tooth number can be used to provide the data
for this selection. Another way to maintain an appropriate library
size is to enforce a highest average yield per blank while
maintaining the inventory production factor within a given
acceptable range. The inventory production factor may take into
consideration the distribution by tooth number data as well. Still
another criterion for sizing the library is to maintain smart
blanks that exhibit a given yield within a given difference factor
(e.g., a standard deviation, or multiple thereof) from a mean of a
normal distribution of a tooth population. Another sizing criterion
is to maintain sufficient smart blanks to facilitate trading off an
average yield per smart blank and an intrinsic cost of the average
restoration, thereby providing the operator with a blank that has a
reasonably good yield but also considers the actual cost of the
material being used.
The above are merely illustrative ways of maintaining a smart blank
library in a cost-effective, demand-driven manner. Preferably, the
sizing of the library (e.g., the selection of which blanks that the
library will include) is done as an automated (computer-assisted)
process, although this is not a requirement taking into
consideration one or more of the above-described process variables.
Generalizing, according to a feature of the invention, there are
many possible criteria that may be used to determine the number
(and possibly the types) of smart blanks to maintain in a given
assemblage. In a preferred embodiment, the goal of optimizing yield
typically is an important factor.
It is now assumed that a smart blank library is being maintained
(preferably according to one or more of the inventory techniques
described above), and that a restoration is ready to be designed.
The following description provides further details of a
representative algorithm for selecting a smart blank in the library
that is "closest" to the restoration being designed R. Without loss
of generality, it is assumed that the restoration R is described in
3D by a closed polygon mesh or, more generally, by any other closed
parameterized surface, such as Non-Uniform Rationale B-Spline
surface (NURB). FIGS. 4 and 5 illustrate two such restorations 402
and 502. Of course, these shapes are merely exemplary. Continuing
with the algorithm, it is assumed that each available blank B.sub.i
in the library also is defined by a closed parameterized surface
representation, where the size of the library is m. According to a
preferred embodiment, a subset {B.sub.1, B.sub.2, . . . B.sub.n }
of n blanks is then selected, where each of the elements in the
subset satisfies the following condition: R.OR right.B.sub.i, for
i=1, . . . n. It should be noted that this condition is met only if
there exists a relative transformation between R and B such that no
point on R is visible from any vantage point outside of B. Stated
another way, a blank that satisfies this condition is said to
"contain" the restoration. Then, the blank of the subset with the
smallest volume is selected as the blank from which the restoration
R will be milled or machined. In particular, because each of the
blanks of the subset contains the restoration, the one with the
smallest volume will necessarily produce the highest yield. The
above-described example is preferred, but variants are within the
scope of the invention. Thus, instead of selecting the blank of the
subset with the smallest volume (and thus the highest yield), an
alternative would be to choose the blank with the second highest
yield (for example, because inventory of the first blank may be too
low, because the first blank is made from a material that is more
costly than the material of the blank with a next highest yield,
and so forth). As another alternative, instead of selecting the
blank of the subset with the highest yield, a blank that has an
acceptable yield may be chosen.
The above are merely representative examples. Any particular
selection criteria (e.g., based on yield, productivity, cost, tooth
distribution, or combinations of such variables) may be used to
facilitate the smart blank selection process once the subset
{B.sub.1, B.sub.2, . . . B.sub.n } satisfying the containment
condition has been determined.
A computer or computer system as illustrated in FIG. 3 preferably
is used to facilitate the above-described algorithm and selection
process. An illustrative computer 300 comprises Intel-commodity
hardware 302, suitable storage 303 and memory 304 for storing an
operating system 306 (such as Linux, W2K, or the like), software
applications 308a-n and data 310, conventional input and output
devices (a display 312, a keyboard 314, a mouse 316, and the like),
devices 318 to provide network connectivity, and the like. Using a
conventional graphical user interface 320, an operator can select
from a menu 322 given criterion by which the smart blank selection
is to be effected, or create a custom criterion using one or more
of the above-described variables (or other factors). In use, it is
assumed that a given geometry of the designed restoration is made
available to the computer system. The system has knowledge of the
unique geometries of each of the smart blanks then available from
the library. Using a given criterion (which the operator can select
or that may be a default), the system then selects the smart blank
from the available blanks that satisfies the given criterion, or
that satisfies the given criterion within a given acceptance
factor. As noted above, the present invention enables the operator
to select the smart blank from the subset based on the factors it
deems appropriate and suitable for its particular purposes.
As described above, the computer-implemented smart blank selection
process first determines the subset {B.sub.1, B.sub.2, . . .
B.sub.n } of smart blanks that satisfy the containment condition.
The subset determination for two different restorations given a
smart library of two blanks 102 and 104 is illustrated in FIGS.
4-6. As seen in FIG. 4, the restoration 402 is containable within
smart blank 102 but not within smart blank 104. Thus, for this
particular restoration, only smart blank 102 would be a candidate
for the final selection, i.e., only smart blank 102 is in the
subset. In FIG. 5, however, the restoration 502 is containable
within both smart blank 102 and smart blank 104; as a consequence,
both blanks are candidates for the final selection, i.e., both are
in the subset. In the preferred embodiment as has been described
above, the smart blank of the subset with the lowest volume (thus,
the highest yield) is then selected for use in milling the
restoration. With respect to restoration 402, this condition does
not matter (at least in this example), as blank 102 is the only
blank in the subset. With respect to restoration 502, however,
there are two choices. Accordingly, as seen in FIG. 6, smart blank
102 is used for the manufacture of restoration 402 while smart
blank 104 (the one with the smallest volume) is used for the
manufacture of restoration 502.
The following describes one computer-implemented technique for
making a smart blank assemblage, although any particular technique
(such as casting or forging) may be used. In general, a shape for
the sets of smart blanks may be selected according to a particular
application. Thus, for example, for each set, multiple (one hundred
or more) cases are evaluated, where a digital impression is made of
each preparation, for each type of preparation and for each tooth
number in the American standard tooth numbering scheme. For each
such preparation, an ideal crown or coping designed for that
preparation is desired to be pre-formed as a smart blank, as
described above. A percentage completed factor C is chosen. A
standard mill blank (typically a block or cylinder) is then
selected. The volume of material V to be removed from the standard
mill block is then determined based on the dimensions of the mill
block and the model of the final crown or coping to be milled. A
target material removal volume U is calculated by U=CV/100. By way
of example, V may be 100 mm.sup.3 and C may be 60%, then U=60
mm.sup.3. The yield for the particular smart blank is then equal to
100%-C.
A standard mill blank (FIG. 7) may be partially milled or machined
to create the smart blank. Similarly, the milling or machining
process may be simulated, e.g, by a digital processor that is
suitably programmed with computer software. The milling procedure
is performed on a standard mill blank and the milling or machining
process terminated when the amount of material that has been
removed has reached or exceeds U. This is illustrated in FIG. 8. In
each case, a series of partially machined crowns or copings may be
formed. A number n of test cases will result in n shapes.
A tolerance percentage factor T may be selected. A subset of the
shapes determined above may be selected based on criterion such as:
for each test case, there must exist in the shape library a shape
where no more than TV/100 volume of material must be removed where
V is the volume of the shape from the shape library. Accordingly,
the larger the tolerance percentage factor T, the smaller the
subset. Based on the C and T parameters and n test cases, a set of
m shapes where 0<m<=n may be formed, in which the m shapes
comprise a smart mill blank library. Each shape may be mass
produced according to the shapes determined above.
As noted above, an integrated milling attachment (the holder or
sprue) is included with each shape to provide attachment for the
milling and machining process. The attachment may be formed from
the same or other material as the smart mill blank.
For each smart mill blank, a partial or a full three-dimensional
(3D) model or computer aided design (CAD) model for the shape and
attachment may be recorded and associated with the smart blank. The
3D and CAD model information may be useful for final milling of the
smart blank.
As noted above, an illustrative embodiment includes a process in
which a proposed restoration is digitally scanned, using a 3D data
acquisition technique. An optimum coping to fit on top of the
restoration may then be determined via a computer-based matching
algorithm. Every dimension (or, optionally, certain key dimensions)
of the coping are determined from the digital data. This shape is
compared with the library of smart mill blanks, and a smart blank
selected for which conditions are satisfied. As used herein, a
selection may be computer-generated, or the operator may be
provided with an indication of which smart blanks "best" fit the
design. In particular, the smart mill blank may be selected so that
the desired coping fits entirely within the smart mill blank and so
that the volume difference between the coping and smart mill blank
is minimized, i.e., so that the yield is optimized.
According to another embodiment, the smart mill blank library
comprises mill blanks for one or more of the following: molars,
pre-molars, bicuspids, canines, upper central incisors, upper
lateral incisors and lower incisors, along with some size variation
allowed for different patients. In addition, the library may also
use as an input variable the ethnicity and sex of the patient.
Using the chosen smart mill blank as a starting point, the amount
of material cut off may be minimized, thereby optimizing yield. The
smart mill blank library also provides for reduced quicker
machining time and reduced recovery process. The blanks may be
formed from precious, semi-precious, non-precious metals, metal
alloys, composite materials, or any other material suitable for
dental applications. Where precious metal may be used, the
invention provides much more viable alternative from an economics
point of view by reducing the amount of material that is wasted and
recovered.
In still another embodiment, the smart mill blank library comprises
a series of blanks made up of a generally convex or concavo-convex
upper surface attached to a concave lower surface, with an
integrated milling attachment with an orientation-specific
attachment key for the milling machine. A variety of combinations
may be formed with different upper surfaces attached to different
lower surfaces to form a large library of smart blanks. FIG. 9B
illustrates a representative library of this type.
In yet another embodiment as illustrated in FIG. 9B, the smart mill
blank library comprises a set of partial spherical shells of
different sizes and thicknesses. Each shell may include an
integrated milling attachment. The attachment may have an
orientation-specific attachment key for a milling machine. The
digitally produced coping may be machined from a selected blank,
for which the cut-off material is minimized during the machining
process.
In a still further embodiment, the smart mill blank library
comprises a series of flattened dimpled spherical solids of
different sizes and thicknesses. Each solid may have an integrated
milling attachment with an orientation-specific attachment key for
the milling machine.
According to another embodiment, the smart mill blank library
comprises a set of mill blanks appropriate for copings for one of
any one of different classes of teeth, such as molars, premolars,
bicuspids, canines and incisors.
In a further embodiment, the smart mill blank library comprises a
set of mill blanks appropriate for crowns for one of any one of
different classes of teeth, such as molars, premolars, bicuspids,
canines and incisors.
Another embodiment of the invention is a smart blank library
comprising a set of mill blanks appropriate for copings for many
different classes of teeth, such as molars, premolars, bicuspids,
canines and incisors, along with size variations in each class.
In another embodiment, the smart mill blank library comprises set
of different blanks that are selected to enable all possible cases
to be milled from one of the mill blanks. The general shapes of the
mill blanks may be selected so that a difference in volume between
the desired coping and at least one library blank is determined to
be less than a predetermined tolerance. The tolerance may be
determined according to economic or other reasons.
In still another embodiment, the smart mill blank library comprises
two sets of blanks: a set of smart crown mill blanks to be used to
mill full crowns; and a set of smart coping mill blanks to be used
to mill copings. This is illustrated in FIGS. 9A and 9B. Each set
is determined by examining multiple real cases and partially
forming a standard mill block to make the desired coping or crown.
By setting a criterion of a certain percentage of material loss
that is permitted in completing the machining or milling, a subset
of those partially machined or milled blanks is selected, and those
shapes are used for the smart mill blank library.
While various embodiments of the invention have been described, it
will be apparent to those of ordinary skill in the art that many
more embodiments and implementations are possible and modifications
may be made that are within the scope of the invention. It should
be appreciated that the apparatuses and methods of the present
invention are capable of being incorporated in the form of a
variety of embodiments without departing from its spirit or
essential characteristics. The described embodiments are to be
considered in all respects only as illustrative and not
restrictive.
As noted above, materials used to make the prostheses typically
include gold, ceramics, amalgam, porcelain and composites. For
dental restorative work such as fillings, amalgam is a popular
choice for its long life and low cost. Amalgam also provides a
dental practitioner the capability of fitting and fabricating a
dental filling during a single session with a patient. The
aesthetic value of amalgam, however, is quite low, as its color
drastically contrasts to that of natural teeth. For large inlays
and fillings, gold is often used. However, similar to amalgam, gold
fillings contrast to natural teeth hues. As noted above, in the
present invention, the smart blanks may be formed of any type of
material normally used for dental restorations.
In the embodiments described above, each of the smart blanks in the
library has a geometry that differs from the geometry of other
smart blanks in the library by other than scaling. This is a
preferred approach, but it is not always a requirement.
As noted above, preferably both the smart blank inventory
management process and the smart blank selection process are
automated, i.e., under the control of a suitably programmed
processor or other controller. While certain aspects or features of
the present invention have been described in the context of a
computer-based method or process, this is not a limitation of the
invention. Moreover, such computer-based methods may be implemented
in an apparatus or system for performing the described operations,
or as an adjunct to other dental milling equipment, devices or
systems. This apparatus may be specially constructed for the
required purposes, or it may comprise a general purpose computer
selectively activated or reconfigured by a computer program stored
in the computer. Such a computer program may be stored in a
computer readable storage medium, such as, but is not limited to,
any type of disk including optical disks, CD-ROMs, and
magnetic-optical disks, read-only memories (ROMs), random access
memories (RAMs), magnetic or optical cards, or any type of media
suitable for storing electronic instructions, and each coupled to a
computer system bus. The computer may be connected to any wired or
wireless network. Further, the above-described functions and
features may be implemented within or as an adjunct to other known
dental milling equipment, devices or systems.
Further, while the above written description also describes a
particular order of operations performed by certain embodiments of
the invention, it should be understood that such order is
exemplary, as alternative embodiments may perform the operations in
a different order, combine certain operations, overlap certain
operations, or the like. References in the specification to a given
embodiment indicate that the embodiment described may include a
particular feature, structure, or characteristic, but every
embodiment may not necessarily include the particular feature,
structure, or characteristic.
* * * * *